Question about acoustic pickups please help?

Hi I have self taught myself acoustic guitar and have a question about
guitar pickups. Now I play just strictly acoustically but after going
into the music store and playing just a cheap acoustic electric
through an amp makes me wanting to add a pickup.

Since I have no knowledge on this and cant get the answers im looking
for online please help.

I am looking into getting the k and k western pure mini pickup and
attaching it under the bridge plate but I notice all the guitars in
the store have the bass, treble, mid controls on the outside of the
guitar. What is that for, just so you can control it from the guitar
itself and not have to go to the amp? Or are the controls on the
guitar combined with the controls on the amp an advantage? Is there a
disadvantage to not having the controls on the outside of the guitar
or is it just for convenience so I dont have to change it from the
amp. Also I have a seagull artist Rosewood is this a good choice
pickup?